New York City police and animal experts were waiting to see if the dolphin would leave the polluted canal on its own during the evening's high tide. / Richard Drew, AP

by Michael Winter, USA TODAY

by Michael Winter, USA TODAY

An injured dolphin that was stranded in a polluted industrial canal in Brooklyn has died, according to news reports.

The adult mammal, which was bleeding from a wound to its dorsal fin, stopped moving about 5:30 p.m. Friday after it became wedged between a rock and a pillar below the Union Street Bridge, CBS New York reports.

The common dolphin was first spotted about 9:30 a.m. Friday swimming slowly around the shallow, narrow Gowanus Canal, The New York Times says. Twitter lit up with similar reports three hours later.

The dolphin's plight attracted onlookers.

"It's really struggling; it doesn't look healthy," Amber Marlow, toldThe New York Daily News earlier in the day. "I can see the dorsal fin. It looks mangled."

During the day, police and marine mammal rescuers had discussed how to react. The were waiting for high tide to return about 7:10 p.m., to see whether the dolphin would swim out to New York Harbor on its own or need help.

"If the animal comes on a beach or something, we can definitely respond to it," Rob DiGiovanni, executive director and senior biologist for the Riverhead Foundation for Marine Research and Preservation, told DNAinfo. "But in this case here, when the animal is free swimming, the procedure is to monitor it for another tide cycle or two and see if moves back out again."

He said dolphins and other sea animals frequently enter the canal from New York Harbor but return to sea on their own.

In March 2010, the U.S. Environmental Protection Agency declared the canal a Superfund site, calling it "one of the nation's most extensively contaminated water bodies." It contains PCBs, coal tar waste and heavy metals from decades of being polluted with toxic wastes and sewage run-off.

The EPA held public meetings Wednesday and Thursday nights to discuss its cleanup plan, which includes removing some of the contaminated sediment and capping dredged areas. The cost is estimated at $467 million to $504 million.

The dolphin was seen expelling black sludge as it surfaced.

"It's disgusting. Hopefully we can get it out before it gets worse," Rebecca Rogers-Hawson said as she watched from the Union Street Bridge.

In 2007, an apparently healthy Minke whale appeared around the mouth of canal. Rescue efforts failed, and it died two days later.